Lightning arrester



0a. 16, 1951 w, BECK 2,571,814

LIGHTNING ARRESTER Filed Oct. 20, 1949 WITNESSES: INVENTOR fl/ EdwardF.W.Beck.

BY iTT ZRN Y Patented Oct. 16, 1951 UNITED STATES PATENT OFFICELIGHTNING ARRESTER Edward F. W. Beck, Pittsburgh, Pa., assignor toWestinghouse ElectricCorporation, East Pittsburgh, Pa., a corporation ofPennsylvania Application October '20, 1949, Serial No. 122,437

, 3 Claims. 1

The present invention relates to lightning arresters, and, moreparticularly, to means for preventing shattering or explosion of valvetype lightning arresters in case of failure of the arrester.

Lightning arresters of the valve type consist essentially of a pluralityof spark gap devices, and a plurality of resistance elements or blockshaving valve, or non-linear, characteristics, disposed in seriesrelation in a housing. The spark gap devices normally isolate thearrester from the line to which it is connected, but upon the occurrenceof an excess voltage, such as a lightning surge, the gaps break down andpermit the surge to be discharged to ground through the resistanceblocks, which have low resistance under excess voltage conditions. Afterthe surge has been discharged, the blocks, because of their valvecharacteristic, reduce the power follow current to a small value whichcan readily be interrupted by the series gaps at the first current zero.

In the normal operation of lightning arresters of this type, no gas isgenerated within the arrester, and the housing is tightly sealed toexclude moisture, which has an adverse effect on the electricalcharacteristics of the gaps and valve blocks. If one or more of theblocks fails during a discharge, however, or if the arrester fails tointerrupt the power current for any other reason, and thus loses itsvalve characteristic, the maximum short-circuit current of the system towhich it is connected flows through the arirester to ground. This causesexcessive heating and arcing within the arrester, and large quantitiesof gas are evolved from the block material. This large quantity of gasgenerated very rapidly 'Within the sealed housing causes very highpressures to be built up in a short time within the housing, and theporcelain housing is frequently ruptured or shattered with explosiveforce, in case of arrester failure, causing pieces of the porcelain tobe thrown violently around, endangering adjacent apparatus or personswho may be nearby. Even if rupture of the housing does not occur, thehigh pressure will be held in the housing for a long period, because ofthe very effective sealing means used in modern lightning .arresters.This is an undesirable condition because if the damaged arrester islater opened or broken, the trapped gas may be expelled with greatforce.

The principal object of the present invention is to provide a lightningarrester of the valve type in which shattering or explosion of thehousing,

in case of failure of the arrester, is prevented, or made less violent,by relieving the internal gas pressure.

Another object of the invention is to provide a lightning arrester ofthe valve type in which the housing is immediately vented upon failureof the arrester, to relieve the internal gas pressure and preventbuilding up of explosive pressures within the housing.

A further object of the invention is to provide a lightning arrester ofthe valve type in which continued arcing in an auxiliary gap devicewithin the housing, due to failure of the arrester, causes burning ormelting of a fusible element to vent the housing and thus relieve theinternal gas pressure.

The invention will be more fully understood from the following detaileddescription, taken in connection with the accompanying drawing, thesingle figure of which shows a lightning arrester embodying theinvention partly in elevation and partly in vertical section.

The invention is shown in the drawing embodied in a lightning arresterof unit construction, which may be used either alone or in a multi-unitassembly, with other similar units, for higher voltages. The arrestershown in the drawing is contained in a housing I of porcelain, or othersuitable weather-resistant insulating material. The housing I may beclosed and sealed at the top in anysuitable or usual manner, and isprovided with an upper metal end casting 2,, which may be cemented tothe housing I, to provide for mounting the arrester and for electricalconnection to it.

The arrester elements themselves, which are disposed in the housing,comprise a plurality of spark gap devices 3, and a plurality ofresistance blocks 4 of material having valve or non-linearcharacteristics. The spark gap devices 3 may be of any suitable type,and are shown as comprising electrode members 5 separated by annularresistance spacers 6. The electrode members 5 preferably have buttons 1of high dielectric constant material, such as rutile ceramic, secured tothem to pre-ionize the gaps to improve the surge breakdowncharacteristics of the gaps.

The resistance blocks 4 may be made of any suitable resistance materialhaving valve characteristics, that is, a material which has very highresistance, or is semi-conducting, under normal conditions, but whichhas very low resistance under excess voltage conditions, to permit asurge to be discharged to ground with low discharge voltage across thearrester, and which is capable of again increasin its resistance afterthe surge has been discharged. The blocks 4 are preferably inade ofgranular silicon carbide mixed with a suitable binder, such as sodiumsilicate, and molded to the desired size and shape, and baked. Suchvalve blocks are, of course, well known in themselves.

The valve blocks 4 are assembled in a vertical column in the housing I,the blocks preferably being separated by spacing and centering washers8, which may be made of relatively rigid insulating material withconducting central rivets, or other means for effecting electricalconnection between adjacent blocks. The gap devices 3 are also assembledin a vertical column in the housing, in series relation with the valveblocks 4, and the column of gap devices is preferably above the columnof valve blocks. The structure so far described is more Or lessconventional, and is to be taken as illustrative of any lightningarrester of the valve type.

The bottom of the housing I is closed and sealed by a metal cap member9, which may be sealed to the housing I in an suitable manner. In theconstruction shown in the drawing, the cap member 9 has a peripheralflange l which is soldered to a metal ring II which encircles the lowerend of the housing I and is soldered to a metallic glaze on the surfaceof the porcelain, as indicated at I2. An annular metal bottom castingI3, having a central opening I4, is placed over the bottom of thehousing I covering the cap member 9, and is cemented to the housing asindicated at I5.

The cap member 9 has a central opening l6, and a fusible element or discI! covers the opening it and is soldered, or otherwise fastened, to thecap member 9 so as to normally close and seal :the opening [6. The discI! may be made of lead or other suitable metal or alloy of low meltingpoint. An annular resistance spacer I8 rests on the disc I! within thehousing I, and an electrode member I9 rests on the spacer l8 and isspaced thereby from the disc H to form an auxiliary spark gap devicewith the disc ll. The

electrode member I9 is preferably a metal disc with a central projectingelectrode portion 20,

which may be welded to the disc or formed intea metal plate 24 securedto the end casting by screws 25 to cover and protect the fusible disc H.The plate 24 is provided with a plurality of holes or openings 25 topermit escape of gas from the interior of the housing.

The normal operation of this arrester is similar to that of anyvalve-type lightning arrester. When a lightning surge or other excessvoltage condition occurs, the spark gaps 3 break down to permit thesurge to be discharged to ground through the resistance blocks 4, andafter discharge of the surge the blocks reduce the power follow currentto a small value which can readily be interrupted at the first currentzero by the gaps. The presence of the auxiliary gap at the -bottom ofthe arrester does not affect the sparkover or breakdown characteristicsof the arre ter, since the 60 cycle, or normal-frequency, voltagedistribution across the gaps 3, is determined by the resistance spacers6, which are in parallel with the gaps, and the impulse or surgebreakdown is determined by the electrostatic field surrounding the gaps.Thus, when the breakdown voltage of the arrester is reached, the gapdevices 3 break down and, in effect, cascade the auX- iliary gap tocause it to are over.

The are in the auxiliary gap, in a normal operation of the arrester,does not last for more than a half-cycle, and this brief arcing does notaffect the fusible disc II. In case of failure of the arrester, however,the power current is not interrupted, and continued arcing occurs bothin the auxiliary gap and in other parts of the arrester. This continuedarcing in the auxiliary gap, which may be very intense because of thehigh current which will usually occur, rapidly burns through or meltsthe fusible disc I1, opening the central opening I6 in the cap member 9.Thus the housing I is vented, and the gas which is generated within thehousing can escape through the opening 2| in the electrode member I9,the opening IS in the cap member 9, and the holes 26 in the plate 24.Since the fusible disc I! will be melted through very rapidly as aresult of continued arcing in the auxiliary gap, the housing is ventedto relieve the internal gas pressure within a very short time afterfailure occurs, and the gas generated within the housing is permitted toescape, so that dangerously high pressures cannot be built up in thehousing, and shattering or explosion of the housing is prevented, ormade less violent.

It should now be apparent that a lightning arrester of the valve typehas been provided in which shattering or explosion of the housing, in

in its broadest aspects it includes all equivalent embodiments andmodifications which come within the scope of the appended claims.

I claim as my invention: 1. A lightning arrester comprising acylindrical housing of insulating material, a plurality of spark gapdevices and a plurality of valve-type resistance blocks disposed in acolumn in the housing, metal cap means closing and sealing the bottom ofthe housing, said cap means including a central fusible element, and anelectrode member below said column and spaced from said fusible elementto form a spark gap therewith, the fusible element being adapted to burnthrough and vent the housing upon continued arcing in the last-mentionedspark gap.

2. A lightning arrester comprising a cylindrical housing of insulatingmaterial, a plurality of spark gap devices and a plurality of valve-typeresistance blocks disposed in a column in the housing, metal cap meansclosing and sealing the bottom of the housing, said cap means includinga central fusible element, a resistance spacer member resting on the capmeans, and an electrode member below said column, said electrode memberbeing spaced by the spacer member from said fusible element to form aspark gap there- 5 with, the fusible element being adapted to burnthrough and vent the housing upon continued arcing in the last-mentionedspark gap.

3. A lightning arrester comprising a cylindrical housing of insulatingmaterial, a plurality of spark gap devices and a plurality of valve-typeresistance blocks disposed in a column in the housing, a metal capmember secured to the bottom of the housing and sealed thereto, said capmember having a central opening, a fusible element secured to the capmember to close, and seal the opening, a. resistance spacer memberresting on the fusible element, and an electrode member below saidcolumn, said electrode member being spaced by the spacer member fromsaid fusible element to form a spark gap therewith,

6 the fusible element beingadapted to burn through and vent the housingupon continued arcing in the last-mentioned spark gap.

EDWARD F. W. BECK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,642,241 Golladay Sept. 13, 19272,179,297 Johnson Nov. 7, 1939 2,296,708 Earle Sept. 22, 1942 152,422,978 Olsen June 24, 1947

